Autoregulation of Cortical Blood Flow in Response to Phenylephrine Induced Hypertension in the Normocapnic and Hypercapnic Cat
The purpose of this research was to determine the degree of autoregulation of cortical blood flow in the cat, and to evaluate the usefulness of the heated thermocouple technique for measurement of local cortical blood flow. We determined the relationship between local flow and voltage output from our thermoelectric flow probe by in vitro experiments with an artificial kidney. We measured local cortical blood flow in 17 cats during episodes of phenylephrine-induced hypertension, under conditions of normocapnia and, in some cases, hypercapnia. Arterial blood pressure and voltage output from the flow probe thermocouples were recorded continuously with a Physiograph-six monitor. We found the heated thermocouple flow probe to be useful for qualitative description and for estimation of relative changes in local cortical blood flow, The relationship between the flow probe thermocouple voltage and local flow was shown to be a hyperbola. We found active regulation of local cortical blood flow in the presence of acutely induced hypertension. This autoregulation does not completely prevent change in local cortical blood flow but it does limit the change. Within the autoregulatory range, an increase in mean arterial blood pressure of 10 percent was associated with an increase in local cortical blood flow of 8 percent. This is in agreement with other studies of cortical blood flow autoregulation in the cat, and represents less complete autoregulation than is found in other species. Breakthrough of autoregulation was found in some cats with mean arterial blood pressures of 180-230 mmHg. We found intact autoregulation of local cortical blood flow in the hypercapnic cat. The upper arterial blood pressure limit of autoregulation was apparently shifted downward from the normocapnic level by hypercapnia.
Veterinary Physiology, Blood Flow Velocity -- veterinary Hypertension -- veterinary Phenylephrine Cats -- physiology Hypercapnia -- physiology
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